Add unit tests for refcounting of iterated-over cypclass

tests/run/cypclass_builtin_dict.pyx

@@ -744,3 +744,29 @@ def test_iterator_refcount():
         return -11
 
     return 0
+
+cdef cypdict[Index, Value] pass_along(cypdict[Index, Value] d):
+    return d
+
+def test_iteration_refcount():
+    """
+    >>> test_iteration_refcount()
+    0
+    """
+    d = cypdict[Index, Value]()
+    if Cy_GETREF(d) != 2:
+        return -1
+
+    for key in d:
+        pass
+
+    if Cy_GETREF(d) != 2:
+        return -2
+
+    for key in pass_along(d):
+        pass
+
+    if Cy_GETREF(d) != 2:
+        return -3
+
+    return 0

tests/run/cypclass_iteration.pyx

+# mode: run
+# tag: cpp, cpp11, pthread
+# cython: experimental_cpp_class_def=True, language_level=2
+
+from libcpp.vector cimport vector
+
+cdef cypclass Value:
+    __dealloc__(self) with gil:
+        print("Value destroyed")
+
+cdef cypclass Stack:
+    vector[Value] vec
+    void push(self, Value v):
+        self.vec.push_back(v)
+    Value pop(self) except NULL:
+        if self.vec.size() > 0:
+            value = self.vec.back()
+            self.vec.pop_back()
+            return value
+        else:
+            with gil:
+                raise IndexError("Stack is empty")
+    vector[Value].iterator begin(self):
+        return vec.begin()
+    vector[Value].iterator end(self):
+        return vec.end()
+
+def test_value_refcount():
+    """
+    >>> test_value_refcount()
+    Value destroyed
+    0
+    """
+    v = Value()
+    s = Stack()
+    if Cy_GETREF(v) != 2:
+        return -1
+    s.push(v)
+    if Cy_GETREF(v) != 3:
+        return -2
+    s.push(v)
+    if Cy_GETREF(v) != 4:
+        return -3
+    s.push(v)
+    if Cy_GETREF(v) != 5:
+        return -4
+    v2 = s.pop()
+    if Cy_GETREF(v) != 5:
+        return -5
+    del v2
+    if Cy_GETREF(v) != 4:
+        return -5
+    v2 = s.pop()
+    del v2
+    if Cy_GETREF(v) != 3:
+        return -6
+    v2 = s.pop()
+    if Cy_GETREF(v) != 3:
+        return -7
+    del v2
+    if Cy_GETREF(v) != 2:
+        return -8
+    try:
+        v2 = s.pop()
+        return -9
+    except IndexError as e:
+        pass
+    return 0
+
+cdef Stack pass_along(Stack s):
+    return s
+
+def test_stack_refcount():
+    """
+    >>> test_stack_refcount()
+    0
+    """
+    s = Stack()
+    if Cy_GETREF(s) != 2:
+        return -1
+
+    for key in s:
+        pass
+
+    if Cy_GETREF(s) != 2:
+        return -2
+
+    for key in pass_along(s):
+        pass
+
+    if Cy_GETREF(s) != 2:
+        return -3
+
+    return 0
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